UN officials say alleged chemical weapons attacks, which Syria's opposition says killed hundreds near Damascus, were a "serious escalation". How should the world respond?

Deputy Secretary-General Jan Eliasson made the comments after briefing an emergency UN Security Council meeting about Wednesday's incident.

Opposition activists said that more than 1,000 people were killed after government forces launched rockets with toxic agents into the Damascus suburbs in the Ghouta region early on Wednesday.

The Syrian government has denied the allegations, describing them as "illogical and fabricated". The Syrian army said the opposition made up the claims to divert attention from the huge losses its forces had suffered recently.

Below, experts discuss how the world should respond to the latest developments.

We must intervene against Assad in this conflict

Dr Alan Mendoza, founder of the Henry Jackson Society

The latest developments merely confirm something I have believed for a long time, which is that we must intervene against [Syrian President Bashar al-] Assad in this conflict.

These developments are important because they show Assad believes he can act with increasing impunity and get away with literally anything, any human rights abuse, any breach of international law.

And if we don't stop him at this point, we're going to regret that when he moves to the next level.

Now the issue is we're not going to get international co-operation because China and Russia have declared already that they are backing Assad in this fight.

So the idea that you're going to get an international coalition through the UN to do this just isn't going to happen. However, it's quite possible for a "coalition of the willing" to come together and [one way that could work] would be arming the rebels, which is already sort of happening on a covert basis.

That does, of course, have risks in terms of who receives the weapons. There's a large and growing Islamist component within the rebel camp and that's obviously not a set of people we wish to be arming.

So you have to pick and choose your people very carefully. There are moderates within the Free Syrian Army (FSA), for example, who could be the targets of legitimate arms supply. That would also have the advantage of strengthening moderates amongst the rebels, which would help a pro-Western stance in any subsequent post-Assad government.

Alan Mendoza

Chief advisor to the All-Party Parliamentary Group on Transatlantic and International Security

The second way of intervening at this stage, which I think is becoming increasingly viable considering discontent about arming the rebels, is air strikes against the regime. This is a relatively cost-free measure, [and] in terms of military superiority, we have that.

The idea here would be to degrade his military capability and force him to understand that the only way this conflict can be resolved is by negotiation, rather than through the violence we've seen thus far.

The longer it drags on, the more Assad needs to face the issue that it will be outright removal that will happen [rather than negotiated settlement]. There's a closing window for him now.

The more atrocities he commits, the greater the improbability of him being able to keep his regime around. There's only so much blood someone can spill before it becomes completely unconscionable to deal with them. If this continues, there's going to be a need to replace the regime full stop. You can't allow these human rights abuses on a regular basis, on an increasing basis, to become the norm, particularly given the message it sends to others as well.

Western intervention will only serve to escalate a conflict that is leading to the dissolution of a key Arab nation

Dr Halla Diyab, film-maker, broadcaster and activist

What do we mean when we say Western intervention? Does it mean supplying small arms and non-lethal assistance? Is it a no-fly zone? Or is it boots on the ground?

These are crucial questions that western governments must take into consideration. Until now, there is little evidence to show that they have done their homework. The US administration is struggling to know which groups among the opposition it should support.

The truth is Western intervention will only serve to escalate a conflict that is leading to the dissolution of a key Arab nation in the Middle East, and by extension fuel a regional conflict that shows little sign of ending.

If the West were to throw its hat into the ring, then whatever hopes the US, Britain or other EU member states may have to play a constructive role in the future of Syria have been ruined.

The West will be regarded as entering a proxy war against Russia, Iran and Hezbollah. Inside Syria itself, ethnic and religious groups such as the Alawites, Shia and many Christians will see the West as supporting an insurgent war against them and their interests.

It was never the intention of the West to support a sectarian war, but this is exactly what it is about to do. Even though advocates of intervention still say this is about bringing down the Assad regime, those days are long gone. The West should ask itself: what metrics does it intend to judge success?

Dr Halla Diyab

More worryingly, the West has absolutely no strategy for life after Assad, if and when that happens. There is obvious concern over the possibility to get bogged down in an Iraq or Afghanistan-style war, but once the West intervenes, in whatever form this may take, just how long is it prepared to stay committed to the "liberation of Syria"?

There are, as of yet, no reliable rebel groups who are prepared to unite with other forces and follow a non-sectarian agenda. There are no men standing ready to form a government. The leading members of Syria's external opposition may wear smart suits and speak forcefully, but they fail to gather the support required to build a viable administration.

The reality is that as long as Iran and Russia maintain the arms race to keep Assad in place, the West can expect to become involved in a long and drawn-out game of one-upmanship, which will only produce religious and ethnic cleavages that will take years to fill. Lebanon's own civil war lasted 15 years and it left an imprint that has still not been erased.

The West is not looking where it wants to leap, and it does so at its danger.

The UN Security Council should refer the Syria situation to the International Criminal Court

Lama Fakih, researcher at Human Rights Watch

Yesterday's alleged chemical weapons attack in Eastern and Western Ghouta, outside Damascus, provided some of the most shocking and cruel images yet seen in Syria's two-year-old civil war.

But the attack, which killed several hundred people including many children, just adds to a death toll that long ago exceeded 100,000. It is yet another example of massive civilian killing that has been tolerated by an international response that has substituted handwringing for effective policy that could save lives.

We now need urgent action from the UN Security Council and other key players.

First, the Council should demand that the Syrian government give the United Nations chemical weapons inspection team - currently in Damascus - immediate access to the sites of the reported chemical attacks, while evidence can still be collected. The UN Commission of Inquiry into human rights and humanitarian law violations should also be given access to establish who is responsible.

Lama Fakih

Syria and Lebanon researcher at Human Rights Watch

Has conducted research missions in Syrian governorates of Aleppo, Idlib, Latakia, and Raqqa to cover both government and opposition abuses

At the same time, both the government and opposition forces must grant full and unhindered urgent access for humanitarian and medical workers to provide badly needed medical care and humanitarian support to affected populations.

And if there is ever to be an end to the cycle of impunity that fuels the killings, the UN Security Council should refer the Syria situation to the International Criminal Court (ICC) to ensure justice for all those responsible for the many war crimes and crimes against humanity committed in this war.

We need to bring down the rhetoric from [a] 'red line' or military intervention

Lord Mark Malloch Brown, former deputy secretary general of the UN

[The chemical weapons inspectors] are a few miles away [from the alleged attack sites] geographically but possibly a million miles away diplomatically because what needs to happen is for the Security Council to unequivocally focus on access for these inspectors.

No report they do on other historic incidents is going to have any credibility if this goes un-investigated.

We need to bring down the rhetoric from [a] "red line" or military intervention, to try and find common ground that we can agree on with the Russians and the Chinese, which is: "Let's establish the facts. Was this an astonishing government attack, of extraordinary brutality against civilians, or was somebody else responsible?"

And then move on from there. At the moment, this is already morphing into "What next?" And that, of course, immediately raises the hackles of the West's opponents on the Security Council, risking therefore, an inspection. And without an inspection, it's going to be a series of unproven charges and counter-charges between the different sides.

Lord Mark Malloch Brown

Deputy secretary general and chief of staff of the UN under Kofi Annan in 2006

Labour peer and now chairman of Europe, Middle East and Africa at FTI Consulting

[Regarding intervention], the analogy may be the Balkans, where for a long time diplomats dug their heels in against intervention. Then there were catalytic moments where what happened in Srebrenica, and what was happening in Sarajevo, swept that aside - and you saw an extraordinary turn of direction.

And while there probably isn't a single event or a single moment [that may alter the course of events], I think the Assad government are badly misreading the West and particularly the US if they think that they somehow now got a blank chequebook to commit any type of atrocity and for it to go un-responded to.